In Defence Of The Slippery Slope Argument

Two men stand on either side of a table. Neatly aligned on top of the table stands a row of dominoes, leading from the edge of the table to the centre, where a small red button sits, labelled ‘LAUNCH NUKES’.

‘If I topple this first domino’, the first man says, ‘That will knock over the second one, and so on, until the last one falls on this red button, and we launch the nukes.’

The second man ponders this for a moment, and then has an a-hah moment and snaps his fingers, saying ‘that’s a slippery slope fallacy!’.

The first man accepts the challenge: ‘One way to find out’. He topples the first domino, and surely enough, a chain of events sees the whole row of dominoes topple one after the other, until the final domino falls onto the button. And then nothing happens. The domino wasn’t quite heavy enough to press the button down.

The second man walks away laughing, saying ‘I knew Year 11 Philosophy would come in handy, you owe me lunch’.

I get the feeling that a large percentage of the population went to a catholic school and had to pick a Religious Education VCE subject in year 11 and then picked philosophy because it’s the least preachy option available and you get to watch the matrix as part of an assignment, and then they came across this poster of logical fallacies and the only fallacy they remember from the poster is the ‘Slipper Slope Fallacy’.

For whatever reason, despite the fact that the wikipedia page goes into a lot of detail about how the slippery slope argument differs from the slippery slope fallacy, people have assumed they are one and the same.

The slipper slope argument goes like this:

• We don’t want Z to happen
• A will cause B with a certain likelihood
• B will cause C with a certain likelihood
• …
• Y will cause Z with a certain likelihood

And the conclusion is that if the product of those likelihoods is a large enough number, we should take seriously the possibility that we really will get to Z if we allow A to happen.

That’s a perfectly reasonable reasonable argument to make. You can debate about what the actual likelihoods are for each link in the chain, and you can debate about how undesirable Z is, but the scaffolding is sound.

The argument only slips (pun not intended) into a fallacy when you claim that each of the probabilities is 100% (with no good evidence) and therefore conclude that A will inevitably cause Z. But I’m not seeing many people using that kind of absolute language when they’re making a slippery slope argument, and even if they were, chances are if you pressed them on it, they’d likely refine their argument to be more reasonable in order meet your standards of rigour. At least that’s been my experience.

But there have been plenty of times where somebody’s told me that I’m making a slipper slope fallacy and I’ve thought ‘well that poster did mention that it was a fallacy and maybe I was too busy watching the matrix to properly understand the poster’s reasoning but I’m sure they’ve thought it all through, so I guess I am committing a fallacy right now and should come back when I’ve got a different argument’.

Granted, it’s usually conservatives who are in the business of making slippery slope arguments, but that’s just because conservatives want to conserve the good elements of society, and that means you’re not going to be seeing many attempts at changing anything coming from the right. If only one side is pushing all the changes, the other side will be tasked with making all the slippery slope arguments when they apply.

Worth noting however that ‘conservative’ != ‘libertarian’ and the conservative UK government has recently pushed to ban certain kinds of porn for certain kinds of people.

Note in that article, point number five is directly making a slippery slope argument:

As campaigner Myles Jackman put it, “Pornography is the canary in the coal mine of free speech: it is the first freedom to die. If this assault on liberty is allowed to go unchallenged, other freedoms will fall as a consequence.”

It’s easy to have your slipper-slope-fallacy detection algorithm running when it comes to things like conservative arguments against gun control and gay rights, but when a law threatens to infringe on freedoms directly affecting you (assuming you care about the freedom to watch porn) all of a sudden the algorithm goes to sleep. I can say I’ve been victim to this selective fallacy detection myself.

In all these cases, there are people who are going to put forward slippery slope fallacies when they instead could be putting forward reasonable slippery slope arguments. But those people are the low hanging fruit and it doesn’t do any good focusing your arguments on what they’re directly saying. Instead, you should steel-man their points (meaning to respond to the strongest version of their argument that you can think of) and think about what the probabilities are of each event causing the next, and whether the total likelihood is enough to warrant their fear that the final domino will indeed fall and hit the button.

After all, if you really studied that philosophy poster close enough, you would have noticed the ‘Fallacy Fallacy’ whose message is that just because somebody is committing a fallacy, that doesn’t mean there isn’t truth to what they’re saying.

Note: A lot of this could be interpreted as a straw-man against people who claim something is a slippery slope fallacy, but the fact that I too was fooled up until just recently about the distinction between the fallacy and the argument makes me think this is a valid criticism.